function unfold(id){
    if (document.getElementById(id).style.display == "block"){
        document.getElementById(id).style.display = "none";
        document.getElementById(id+"img").src="images/plus.png";
    }
    else{
        document.getElementById(id).style.display = "block";
        document.getElementById(id+"img").src="images/min.png";
   }
}